Autophagy, a process in which the lysosomes of cells capture, degrade and recycle cellular contents, such as cytosol and organelles, has been implicated in many diseases such as cancer, ageing, neurodegeneration, innate immunity and programmed cell death. It encompasses several autophagy- related pathways in which cargos are targeted for lysosomal turnover both selectively and non-selectively. The pathways in which cargos are degraded selectively include the cytosol to vacuole transport (Cvt) pathway and peroxisome turnover by micropexophagy and macropexophagy. Pexophagy contributes to virulence in fungal pathogens of plants and humans. Our long-term interest is to understand how the balance between organelle biogenesis and turnover contribute to organelle homeostasis, a phenomenon used by cells to respond to environmental cues. We have chosen to address this problem using peroxisomes and yeast as the model organism. Of the 33 autophagy-related proteins described to date, about half are involved in the core autophagic machinery involved in all autophagy-related pathways, while the others adapt this core machinery for the selective autophagy pathways. Our analysis of pexophagy- specific genes has revealed over half a dozen new proteins that are pexophagy-specific. We wish to elucidate mechanistically how these proteins adapt the autophagy machinery. In addition, we wish to understand the signaling pathways that trigger pexophagy, as well as the cross-talk between the peroxisome biogenesis and turnover machineries. The Specific Aims of the proposal are to focus on the following topics: 1. Signaling events during pexophagy. 2. Nucleocytoplasmic shuttling of pexophagy-specific proteins and its physiological role. 3. Trafficking and role of Atg35 in pexophagy. 4. Ongoing functional analysis of pexophagy-specific proteins. 5. Inactivation and degradation of the docking complex of the peroxisome biogenesis machinery during pexophagy. 6. Connection between peroxisome inheritance and pexophagy. PUBLIC HEALTH RELEVANCE: Our long-term interest is to understand how the balance between organelle synthesis and degradation contributes to the steady-state level of subcellular compartments, such as peroxisomes. This proposal seeks to understand the protein machinery involved in peroxisome degradation in response to environmental cues, focusing on the proteins and mechanisms involved, as well as the coordination between the peroxisome biogenesis and turnover machineries.